How do you build a wood gate that will not sag?

Start with the hinge post

Every gate hangs from one post, and that post takes the gate's weight on a lever every time it swings. A standard fence post set like its neighbors will creep toward the opening within a few years. For a yard gate we use a heavier post, set it deeper than the fence posts with a generous footing, and tie it to the next post with the top rail so the two act together. On wide or heavy gates a steel post sleeved in wood is the surest answer; it does not rot, bend or creep.

The latch post matters less structurally, but it should be plumb and solid so the latch meets the same spot every time.

Build a frame, not a panel

A strong gate is a rectangle of rails and stiles joined at the corners, with the infill boards attached to that frame. The joints are what resist racking. Half-lap joints glued with exterior adhesive and screwed, or mortise-and-tenon joints for a finer gate, hold square far better than butt joints with a couple of screws. Pocket screws with exterior glue are a reasonable middle ground on a simple gate.

Keep the frame proportional. Stiles and rails made from thicker stock than the pickets give the hinges something to bite and keep the gate from twisting when it is slammed.

The brace, and which way it goes

The diagonal brace is the part most often done wrong. A wood brace works in compression: it must run from the bottom corner on the hinge side up to the top corner on the latch side. Gravity tries to drop the latch corner, and the brace, pushing up from the hinge, stops it. Installed the other way, the brace does nothing and the gate sags with a diagonal board in it.

Fit the brace tight into the corners of the frame, not just screwed across the face of the rails, so it bears on wood. On a tall gate, two braces in a Z pattern keep both halves stiff. A cable and turnbuckle running the opposite diagonal is an acceptable alternative where a wood brace would spoil the design.

• Low at the hinge side, high at the latch side.
• Cut to bear tight in the frame corners.
• Check square by measuring both diagonals before fastening infill.

Wood, weight and fasteners

Choose dry, stable lumber: vertical-grain cedar or redwood, or a stable hardwood for a showpiece gate. Green or wet wood will shrink and loosen every joint. Keep the gate as light as the design allows, because weight is what sags gates; thinner infill boards on a stout frame beat thick boards on a light one.

Use stainless or heavily coated screws, pre-drill near the ends so nothing splits, and seal every cut end and the bottom of the frame with finish before assembly. The bottom rail of a gate lives in splashback and is the first thing to go soft.

Hanging it right

Size the hinges to the gate, not to the pickets. Heavy strap or T-hinges with screws that reach through the frame into the post, three of them on a tall gate, hold the weight without working loose. Leave a consistent gap on the latch side and a little clearance at the bottom for winter swelling and uneven ground. Add a stop so the gate closes against something other than its latch, and a self-closing hinge or spring if the gate guards a pool or keeps a dog in.

A gate built this way is heavier to make than a few pickets on two rails, and it is the last gate you will build for that opening.

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